Ecology
Ecology :
The word "ecology" was created in 1866, by
the German biologist Ernst Haeckel, from two Greek words: oikos which means:
house, habitat, and logos which means science. Ecology therefore appears as the
science of habitat, studying the conditions of existence of living beings and
the interactions of all kinds that exist between these living beings and their
environments. It is about understanding the mechanisms that allow different
species of organisms to survive and coexist by sharing or competing for
available resources (space, time, energy, matter). By extension, ecology is
based on related sciences such as climatology, hydrology, oceanography,
chemistry, geology, pedology, physiology, genetics, ethology, ... etc, which
makes it a multidisciplinary science!
Ecological studies conventionally focus on three
levels:
The individual, the population and the community.
• An individual is a specimen of a given species.
• A population is a group of individuals of the same
species occupying a particular territory at a given time.
• A community or biocenosis is all the populations of
the same environment, animal population (zoocenosis) and plant population
(phytocenosis) which live in the same environmental conditions and in close
proximity to each other.
- Each of these three levels is the subject of an
ecological division:
• the individual concerns autoecology: it is the
science that studies the relationship of a single species with its environment.
It defines the tolerance limits and preferences of the species under study with
respect to various ecological factors and examines the action of the
environment on morphology, physiology and ethology.
• the population concerns the ecology of populations
or the dynamics of populations: it is the science which studies the qualitative
and quantitative characteristics of populations: it analyzes the variations in
abundance of various species to find the causes and if possible predict them .
• biocenosis concerns synecology: it is the science
that analyzes the relationships between individuals belonging to various
species of the same group and of these with their environments.
Ecosystem :
An ecological system or ecosystem was defined by the
English botanist Arthur Tansley in 1935.
An ecosystem is by definition a system, that is, a set
of elements in interaction with each other. It is a biological system formed by
two inseparable elements, the biocenosis and the biotope.
- The biocenosis is all the organisms that live
together (zoocenosis, phyocenosis, microbiocenosis, mycocenosis, etc.).
- The biotope (ecotope) is the fragment of the
biosphere which provides the biocenosis with the essential abiotic environment.
It is also defined as the set of abiotic ecological factors (substrate,
"edaphotopic" soil, "climatope" climate) which characterize
the environment in which a specific biocenosis lives.
- The biosphere is the part of the earth's crust where
life is possible. The biosphere includes part of the lithosphere (solid part of
the earth's crust), part of the atmosphere (the gaseous layer surrounding the
earth) and part of the hydrosphere (part of the earth's system made up of
water). The biosphere refers to all of these environments and all the living
things that live in them.
Example: a forest made up of trees, herbaceous plants,
animals and soil.
Ecosystem: forest.
Biocenosis: phytocenosis (trees, herbaceous plants)
and zoocenosis (animals).
Biotope: soil.
Depending on the scale of the ecosystem we have:
- a micro-ecosystem: example a tree;
- a meso-ecosystem: example a forest;
- a macro-ecosystem: example a region.
Ecosystems are often classified by
reference to the biotopes concerned. We will talk about:
• Continental (or terrestrial) ecosystems such as:
forest ecosystems (forests), grassland ecosystems (grasslands), agro-ecosystems
(agricultural systems);
• Inland water ecosystems, for lentic ecosystems of
slowly renewing calm waters (lakes, swamps, ponds) or lotic ecosystems of
running water (rivers, rivers);
• Oceanic ecosystems (seas, oceans).
Ecological niche :
Organisms of a given species can maintain viable populations
only under a certain range of conditions, for particular resources, in a given
environment and for particular periods of time. The intersection of these
factors describes the niche, which is the position the organism occupies in its
environment, including the conditions in which it is found, the resources it
uses and the time it spends there. Organisms can change niches as they
grow.
Example: Common toads inhabit an aquatic environment (feed on algae and debris)
before metamorphosing into adults, where they become terrestrial (feeding on
insects).
Unlike the niche, an organism's habitat is the physical environment in which an organism is found. Habitats contain lots of niches and support many different species.
Example: A forest has a large number of
niches for a choice of birds (nuthatches, woodcock), mammals (wood mice,
foxes), insects (butterflies, beetles, aphids) and plants (wood anemones,
mosses) , lichen).
Environmental factors :
We call "ecological factor" any element of
the environment that can act directly on living beings. Ecological factors
are of two types:
- Abiotic factors: all the physico-chemical characteristics of the environment such as
climatic factors (temperature, rainfall, light, wind, etc.), edaphic (texture
and structure of the soil, chemical composition, etc.), etc.
- Biotic factors: set of interactions that exist between individuals of the same species or different species: predation, parasitism, competition, symbiosis, commensalism, ... etc.
The reactions of living beings to variations in the
physico-chemical factors of the environment concern morphology, physiology and
behavior.
Living things are either completely eliminated, or
their numbers are greatly reduced when the intensity of ecological factors is
close to or exceeds tolerance limits.
A- Law of tolerance (tolerance
interval) :
Enunciated by Shelford in 1911, the law of tolerance
states that for any environmental factor there is a domain of values (or tolerance
interval) in which any ecological process dependent on that factor can proceed
normally. It is only within this interval that the life of a particular
organism, population or biocenosis is possible. The lower limit along this
gradient delimits death from deficiency, the upper limit delimits death from
toxicity. Within the tolerance interval, there is an optimum value, called a
"preferendum" or "ecological optimum" for which the
metabolism of the species or community in question takes place at a maximum
rate.
The ecological valence of a species represents its
capacity to withstand more or less large variations of an ecological factor. It
represents the ability to colonize or populate a given biotope.
• A species with a strong ecological valence, that is
to say capable of populating very different environments and withstanding
significant variations in the intensity of ecological factors, is called
a euryecium.
• A species with low ecological valence will only be
able to withstand limited variations in ecological factors, it is called stenoecia.
• A species with an average ecological valence, is
called mesoecia.
B- Law of the minimum:
We owe to Liebig (1840) the law of the minimum which
stipulates that the growth of a plant is only possible to the extent that all
the elements essential to ensure it are present in sufficient quantities in the
soil. It is the deficit elements (the concentration of which is less than a
minimum value) which condition and limit growth.
Liebig's law is generalized to all ecological factors
in the form of a law known as the "law of limiting factors".
C- Limiting
factor:
An ecological factor acts as a limiting factor when it
is absent or reduced below a critical threshold or if it exceeds the maximum
tolerable level. This is the limiting factor that will prevent the
establishment and growth of an organism in a medium.
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